In evaluating the effects of health behaviors on disease risks, epidemiologic studies face a methodological challenge of assessing individuals' health behaviors accurately. Measurement errors in health behavior assessments are common and could distort analysis results not only quantitatively, but also qualitatively. Biomarkers of health behaviors are useful tools that enable objective exposure assessments in observational studies. We propose a study for establishing biomarkers of health behaviors with a long-term goal of identifying serum protein profiles that objectively indicate the levels of individuals' healthy behaviors (e.g., regular exercise, diet with high intake of fruits and vegetables). Specifically, this project has the following goals: (1) Using MALDI (Matrix Assisted Laser Disorption and Ionization) mass spectrometry technology, measure protein profiles in serum samples, collected at baseline, 3 months, and 12 months of a yearlong randomized exercise-intervention trial; (2) Identify changes in protein profiles that are associated with the exercise intervention and adherence measures; (3) Compare the effectiveness of different data-analytic approaches in the pursuit of Goal (2); and (4) Biologically identify possible biomarkers of regular exercise. These goals will be accomplished utilizing participant samples from an existing randomized one-year exercise-intervention trial (Principal Investigator: Anne McTiernan, R01 CA77572), with 202 participants (100 women, 102 men). The accomplishment of these goals will validate both the MALDI laboratory techniques and the data-analytic methods we have developed through the preliminary work described in Section C, and provide a MALDI-based protein profile as a candidate biomarker of regular exercise levels for use in epidemiologic research.